Priority is claimed to Japanese Patent Application Number JP2005-081438 filed on Mar. 22, 2005, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a wastewater treatment equipment separating materials to be removed (hereinafter referred to as MTBR) containing hydrofluoric acid components from a water to be treated (hereinafter referred to as WTBT).
2. Description of the Prior Art
From the viewpoints of ecology, reduction of industrial wastes and their separation and reuse are currently important themes. Various fluids containing MTBR are included in these industrial wastes.
Although they are described by various words such as sewage, wastewater, and waste liquid, those fluids including water and chemicals containing MTBR will be called wastewater and will be described below. There are cases where this wastewater is reused after becoming a clean fluid due to the removal of the MTBR using an expensive filtration treatment equipment and so on. Furthermore, there are also cases where the MTBR separated from this wastewater are treated as the industrial wastes. Water in particular is discharged to nature or reused after being turned into a clean state by filtration, which meets environmental standards.
Moreover, a copious amount of wastewater is produced during manufacturing processes of a semiconductor device. Among the processes, wastewater containing a fluorine component like hydrofluoric acid is discharged during an etching process. It is known that the balance of ecosystems will be disturbed when wastewater with a high concentration of fluorine components is discharged to nature. Accordingly, it is extremely important industrially to remove fluorine components from wastewater.
On the other hand, a standard value in terms of discharge of wastewater containing fluorine components is set by the Water Pollution Prevention Law, ordinances of local governments, and so on. Specifically, the concentration of fluorine components contained in the wastewater has to be 8 mg/L or lower. Furthermore, there is also a possibility that the total volume control of fluorine components discharged will be carried out.
Numerous removal methods are proposed as the methods for removing fluorine components described above. A method for carrying out biological treatments and chemical treatments in separate treatment tanks as the method for removing fluorine components contained in the wastewater is proposed for instance in Japanese Patent Application Publication No. 2001-54792 (Document 1). Another method for carrying out the removal of fluorine components is described for instance in Japanese Patent Application Publication No. Hei 06-312190 (Document 2). In this method, after preparing a plurality of reaction tanks, a seed agent containing substances in a sol state is formed by adding calcium components to raw water stored in one reaction tank, and fluorine components is treated by adding the seed agent to raw water stored in the other reaction tank. Furthermore, there is also a treatment method for obtaining sludge by chemically precipitating fluorine components contained in the wastewater using polymer flocculants.
However, in the treatment method of wastewater containing fluorine components described in the aforementioned Document 1, since a plurality times of treatment steps of the wastewater is required, increase in a facility scale has been a problem. Accordingly, a cost for the wastewater treatment increases. Furthermore, since the treatment of organic components using living organisms is carried out, difficulties in carrying out a stable wastewater treatment have been a problem.
Furthermore, in the treatment method of the wastewater described in the aforementioned Document 2, since a concentration of fluorine components contained in the wastewater is extremely low, there has been a problem that other treatment steps like chemical precipitation for carrying out a solidification of the obtained fluorine components.
Moreover, a production of sludge in large amounts as an industrial waste has been a problem when removing fluorine components in wastewater by coagulating sedimentation using commercially available macromolecular coagulants. Furthermore, a difficulty in reusing sludge containing a large amount of coagulant has also been a problem.